3.3.4.1 Mass Transport In Animals - Hb

Question 1

Structure and function of Hb

Answer 1

• Hb is a globular protein with a quaternary structure
• 4 polypeptide chains
• an Haem group is associated with each polypeptide chain - where the o2 molecule binds reversibly, forming oxyhaemoglobin.
• Hb required, as o2 has low solubility in water at body temp.

Question 2

How are RBC specialised to maximise transport & exchange of substances

Answer 2

• minimal organelles, so more space for Hb
• biconcave shape maximises SA:V, increasing the rate of diffusion
• cell diameter small, minimises diffusion distance between tissues and RBC

Question 3

Binding of oxygen by Hb

Answer 3

• when the 1st o2 molecule binds to Hb, causes a change in the protiens shape
• makes it easier for other o2 molecules to bind = cooperative binding
• the affinity of Hb for o2 has increased

Question 4

Hb activity in the lungs

Answer 4

• o2 will associate with Hb (load)
• the Hb will be close to 100% saturated with o2
• Hb has a high affinity for o2

Question 5

Hb activity in the active (respiring) tissues

Answer 5

• o2 will dissociate from Hb (unload)
• the Hb will be around 25% saturated with o2
• Hb has a lower affinity for o2

Question 6

Hb activity in the resting tissues

Answer 6

• some o2 will dissociate from Hb (unload)
• the Hb will be around 50-75% saturated with o2.

Question 7

Transport of Co2

Answer 7

• Co2 diffuses from respiring tissues into the blood plasma & then into the RBC
• majority of Co2 reacts with H20 to form carbonic acid. Catalysed by carbonic anhydrase.
• carbonic A, partially dissociates to form H+ and Hydrogen carbonate ions.
• the H+ binds to Hb to form haemoglobinic acid.
• some Co2 is transported:
  Dissolved in blood plasmas or bound to the Hb directly

Question 8

Effect of Co2 on Hb (Bohr Effect)

Answer 8

• Haemoglobinic A, has a different quaternary structure than Hb
• Haemoglobinic A, has a lower affinity for o2 than Hb
• means that o2 dissociates more readily
• supplies o2 more rapidly to respiring tissues
• Bohr effect as a shift of the curve to the right when Co2 concs are higher

Question 9

Hb in different organisms (red curve = human Hb furthest to the left)

Answer 9

• Hb with a higher affinity for o2 than adult human Hb.
• fetal Hb has a higher affinity for o2 than the mothers Hb. Means that o2 will be transferred from mother -> fetas at placenta

Question 10

Hb in different organisms (blue curve = mouse Hb)

Answer 10

• this Hb has a lower affinity for o2 than adult Hb
• because the mouse is smaller + has higher SA:V
• so higher rate of respiration, to maintain its body temperature.